There were no trees inside St Paul's in 1981. The press assembled well before kick-off. We were innocents then, of the present as well as the future. The bride's bulimia (an episode the previous night), the bridegroom's mistress: how could we have known, what gave us the right to know? It was a beautiful day in late July. Nobody could have guessed that the marriage we were witnessing would plant the seeds of monarchy's near destruction.

"Lovely, lovely, lovely," the Washington Post reported next day in a severe case of adjectival exhaustion. "Lovely, lovely, lovely." About 750 million people watched. For a day, all was right with the world. The cathedral's dean, the Very Reverend Alan Webster, addressed us: "Can you see at the back? Now if you have time to sing, do sing because the hymns have been chosen by the prince and not by clergymen and it's almost your duty to sing."

I don't think many of us sang – the invitation made us as sullen and awkward as an infant class – but an exception was certainly Jean Rook, the woman then billed in the Daily Express as the First Lady of Fleet Street. She stood in the pew behind and gave it her all, like Dame Clara Butt.

The national anthem had been given a flashy arrangement by David Willcocks. I wrote at the time that it was like listening to the opposite of freeform jazz, where "one realises with a deepening sense of loss that the saxophonist has left the melody behind and intends to mess about fruitlessly for the next 20 minutes"; that in this case, no matter how complicated the introduction, the tune would arrive in all its dreariness.

The Sunday Times editor, Frank Giles, objected: "I think it's a jolly good tune." But he let the remark stand – he was (and so far as I know still is) a nice, elegant man of a kind you hardly ever see any more. A former diplomat, he'd served in the Moscow embassy in Stalin's day. Looking up his details now, I see he was 20 when the second war broke out, which may have made a difference to how he heard the tune.

We tend to forget this fact of 30 years ago – that the crowds who came to cheer contained so many people who had once seen Lancasters and Spitfires as familiar objects. Aged 50, you would remember the war. Aged 60, you might have fought in it.

As dawn broke over the Mall, young gangs could be heard chanting like football fans, "Lady Di, Lady Di, Lady Di". That seemed like a new kind of British behaviour, ribald and self-mocking. "The line between a joke patriot and a real patriot," as the Spectator wrote, "having grown fainter and finally disappeared." But when the sun rose higher, an older generation came out to sweeten the atmosphere. I heard Maybe It's Because I'm a Londoner and Blaydon Races, neither of them sung within the quotation marks of irony. The singers knew the words. I wrote that it was as if I'd fallen down a magical well into a country peopled by Stanley Holloway, Will Hay and the Crazy Gang.

In 1981, that country wasn't really so far away. British pits still employed a quarter of a million miners, ships stills went down the slipways of several dozen British shipyards, the Rolls-Royces that purred to the front door of St Paul's still had British engines.

We took the most extraordinary things for granted. When Charles and Diana left on their honeymoon they went by special train – one just for them – from Waterloo to Romsey in Hampshire, where they spent three days at the Mountbatten house. Next they flew to Gibraltar to join the royal yacht Britannia for a Mediterranean cruise, with a marine band aboard and nearly 250 officers and crew, the crew as usual in plimsolls so as not disturb the royal rest. Again, just for them.

Did I mind? Did anyone mind? Did the Guardian scowl? I don't remember that we did. (For myself, I loved the Britannia – beautiful lines, built in Clydebank – and nearly cried when in 1997 I went to see her leave the Pool of London on her final voyage.)

Republicanism came out to play and threatened nothing. A few of my friends joined an anti-wedding excursion to France, where they drank lots of wine and handed out leaflets to bemused people in Boulogne. "La classe ouvrière" in Britain was finding it hard to make ends meet, these leaflets said, while at the same "une somme enorme" was being spent on the nuptials of an obscure naval officer and a rich debutante.

If anything, this rather understated the position. Imprisoned IRA men were dying on hunger strike, urban rioting had erupted in several English cities, 2.5 million people (and rising) were on the dole. But at my local Funk the Wedding festival – how polite we were then – a poster saying "Let them eat fishfingers" was the nearest we got to the guillotine.

No change there, you may feel, but at least the temperament of the royal crowd seems different. I walked along the Mall this Thursday. The phrase "media event" doesn't quite capture what was going on. The spectators camped in their tents were certainly there to watch the pageantry, but they were also aware that they existed to be talked to, filmed and photographed.

So there was one group, immobile with their flags and funny hats at the fence, and a constant procession of people behind them holding notebooks and cameras. "Have you come far?" "Are you enjoying yourself?" "All the way from San Diego, really!" We sounded just like the Queen.

In other words, the crowd was there to see and be seen. A jolly bunch of women singing Get Me to the Church on Time had the words in front of them, and tended to stop when the cameras turned off. No need to sneak up on them like Cartier-Bresson.

The modern crowd knows its importance as an actor. Whose death explained it to them? I give you the nervous, unknowing girl at St Paul's 30 years ago. "Lovely, lovely, lovely, lovely, lovely, lovely" (Washington Post).